ES2700127T3 - Procedure for manufacturing a pipe, in particular a brake line or a fuel line for a motor vehicle and said pipe system - Google Patents

Abstract

Process for manufacturing a pipe (10, 70) provided with a flange (40, 40a), in particular a brake pipe or fuel pipe for a motor vehicle, comprising the following steps of the method: providing a pipe (10, 70) comprising an inner tube (20) extending in an axial direction (x), a covering (30) covering the inner tube (20) and an end segment (12) ending in an end surface (11) of the pipe (10, 70); performing a pickling on the end segment (12) along a first segment of pickling (13) until reaching a first layer thickness (Δ1) so that the surface of the end segment (12) produces a first coefficient of friction (μ1) in the region of the first pickling segment (13); performing a pickling in the end segment (12) along at least a second pickling segment (16) to a second constant layer thickness (Δ2) that is greater than the thickness of the first layer (Δ1), so that the surface of the end segment (12) produces a second coefficient of friction (μ2) in the region of the second coating segment (16) which is smaller than the first coefficient of friction (μ1); forming the end segment (12) to form a flange (40, 40a) having a sealing surface (41, 41a), on the front side, and a bearing surface (42, 42a) remote from the sealing surface (41 , 41a), such that the first pickling segment (13) forms the sealing surface (41, 41a) and the second pickling segment (16) forms the support surface (42, 42a), the transition from the first pickling segment (13) to the second pickling segment (16) in the region of the largest outer diameter of the flange (40, 40a).

Description

DESCRIPTION

Procedure for manufacturing a pipe, in particular a brake line or a fuel line for a motor vehicle and said pipe system

The present invention relates to a method for manufacturing a pipe provided with a flange, in particular a brake pipe or fuel pipe for a motor vehicle. The invention also relates to said pipe. Brake lines, also called brake lines, or fuel lines, also called fuel lines, which are used in motor vehicles and can be designed rigidly or flexibly, usually have a multi-layer structure. An inner tube, which usually consists of aluminum or steel, is surrounded by a layer of corrosion protection, which protects it from external influences, which is encased in a cover that generally consists of plastic or is constructed as a layer of lacquer.

For the connection of a pipe of this type, for example, to a brake system unit of a motor vehicle, such as a brake cylinder or a brake booster, the so-called pipe screws or male accessories, which have a passage, are used. to receive the pipe and an external thread to screw into an opening of the unit provided with an internal thread. The pipe is inserted in the passage in such a way that a flange arranged at the end of the pipe, when the pipe screw is screwed into the opening of the unit, presses sealingly against a connection surface located at the bottom of the opening and therefore the screw of the tube in the opening is clamped between the connecting surface and a contact surface. The design of the flange is usually standardized, for example, in accordance with DIN 74 234: 1992-09 concerning hydraulic brake systems; brake pipes, flanges. Pipe screws for fixing pipes are described, for example, in DE 102012108433 B3, DE 4236323 A1, EP 2136119 A1, DE 202014102663 U1 and EP 1624183 A1.

The tubular screw known from DE 10 2012 108 433 B3 is characterized in that two layers of a polyethylene-based dry friction friction reducing film are applied to the contact surface. The pipe screw thus generates a comparatively low coefficient of friction in the region of the contact surface, which ensures that the torsion of the pipeline is prevented by contact with the pipe flange and by the resulting friction. . Because twisting occurs it leads to an unwanted torsional tension in the pipe, which causes the risk of loosening the pipe bolt. A low coefficient of friction is also produced in the area of the contact surface by a double coating on the pipe screw known from DE 202014102663 U1.

The flange of the pipe is produced by a shaping. The end surface of the flange in the axial direction of the pipe acts as a sealing surface and therefore should be as smooth as possible and free of cracks and grooves. Therefore, it is necessary to remove the cover layer in the end segment of the pipe before forming. This separation is usually carried out either by means of a mechanical treatment, by means of a pickling tool, as is known, for example, from documents DE 20214265 U1 and US 2010/0126972 A1, or by means of a roller tool. alternating pressure as known from DE 102013011213 B3, in which the upper layer is removed in the area of the end segment, or by means of laser processing, as is known from DE 29510705 U1, in which Remove the cover layer by means of a laser beam.

Both in mechanical processing by means of pickling tools and in laser processing, the objective of the known processes is to remove the coating layer as much as possible without leaving residues and without damaging the underlying layer of corrosion protection. Above all, waste-free separation is considered essential, since the particles of the coating remaining in the end segment when they are released can represent a significant threat to the reliability of a braking system, as highlighted in the document. DE 102013011213 B3 and DE 29510705 U1.

Furthermore, document WO 98/39137 A1 discloses a method for manufacturing a brake pipe provided with a flange, in which, by laser processing, a protective layer present in the brake line is eliminated before the transformation of the flange. The method provides an inclined transition cut that extends to some extent within the region of the flange. The transition area serves to avoid a sharp edge in the transition from the protective layer to the bare area.

The invention is based on the object of providing a method for the manufacture of a pipe, through which a pipe provided with a flange can be generated which in the installed state counteracts the involuntary detachment of a pipe screw.

This object is achieved by a method according to claim 1 and a line according to claim 8. Preferred embodiments of the invention are defined in claims 2 to 7 and 9 to 11.

The method of the invention for manufacturing a pipe provided with a flange, which is, in particular, a brake line or a fuel line for a motor vehicle, includes the steps of:

Providing a pipe comprising an inner tube extending in an axial direction, also called a pipe core, a coating covering the inner pipe and an end segment terminating at an end surface;

Decap the end section along a first pickling segment up to a first layer thickness, so that a first friction value can be generated with the end segment surface in the first pickling segment

Decap the end segment along a first pickling segment to a first layer thickness so that a first coefficient of friction can be generated with the surface of the end segment in the first pickling segment;

Decap the end segment along at least a second pickling segment up to a second constant layer thickness that is greater than the first thickness, so that the surface of the end segment in the second pickling segment can generate a second pick-up coefficient. friction, which is less than the first coefficient of friction;

The shaping, in particular of a flange, of the end segment to form a flange, having a sealing surface at the end and a bearing surface opposite to the sealing surface, so that the first pickling segment forms the surface of sealing and the second pickling segment forms the bearing surface, wherein the transition from the first pickling segment to the second pickling segment is in the region of the larger outer diameter of the flange.

The pipe according to the invention finds application in particular as a brake pipe or fuel pipe for a motor vehicle application, and includes an inner pipe extending in the axial direction, an inner pipe liner and an end segment ending in an extreme surface. The end segment comprises a flange, which has a sealing surface on the front side and a bearing surface opposite the sealing surface. The coating is selectively withdrawn in the area of the end segment in such a manner as to cause the surface of the end segment on the sealing surface to have a first coefficient of friction and on the bearing surface to have a second coefficient of friction that is less than the coefficient of friction. first coefficient of friction. The coating is reduced in the first pickling segment to a first layer thickness and in the second pickling segment to a second constant layer thickness, which is greater than the thickness of the first layer. The transition from the first pickling segment to the second pickling segment is in the region of the larger outer diameter of the flange.

The invention is based on the knowledge of manufacturing a comparatively high coefficient of friction in the first pickling segment and a comparatively low coefficient of friction in the second pickling segment, by a gradual elimination of the end segment. The friction value, also called the coefficient of friction, is a dimensionless number that is calculated from the measured physical properties and depends on the type and geometry of the surfaces in contact. The test configurations and test procedures for determining friction coefficients or friction coefficients are described in particular in VDA 235 203 and DIN EN ISO 16047: 2005.

After deforming the end segment to form a flange, also referred to as a flange flange, for example, by bending by means of a common crimping tool, the first pickling segment forms the front sealing surface of the flange in the axial direction and the second pickling segment forms the bearing surface of the flange opposite the flange against which, in the installed state, the contact surface of the pipe screw rests. The lower coefficient of friction in the area of the support surface ensures that when the screw of the pipe is screwed, a comparatively smaller friction between the bearing surface of the pipe screw and the contact surface of the flange will occur and thus avoid torsion of the pipe, which would cause undesirable torsional stress. The higher coefficient of friction in the region of the sealing surface ensures a frictional coupling of the flange on, for example, a braking system unit of a motor vehicle and not only contributes to an assembly that prevents torsion of the pipe, but also to a hermetic connection.

In contrast to conventional methods up to now, the invention makes it known that it is not necessary to eliminate the covering layer, that is to say, the coating of the pipe in the entire end segment without residues. Rather, it has been shown that not only is it practical, but also particularly advantageous to leave a residue by selective removal of the coating, at least in the region of the second pickling segment, through which a comparatively low coefficient of friction can be achieved. . Thus, the invention makes it possible to open new paths, since it allows the functional design of the flange, for example, to use conventional pipe screws that do not consume coating and, therefore, are not expensive to manufacture.

In a preferred embodiment of the invention, the first pickling segment extends in the axial direction from a first start point to a first end point. The second pickling segment preferably extends in the axial direction from a second starting point to a second end point. The first start point is preferably on the end surface, while the first end point and the second start point preferably coincide. In the latter case, the first pickling segment extends from the end surface of the pipe to the second pickling segment. The transition from the first pickling segment to the second pickling segment according to the invention is in the region of the larger outer diameter of the flange. However, the first pickling segment and the second pickling segment do not adjoin one another, but may, depending on the configuration of the flange, for example, in the axial direction, be arranged at a distance from each other, so that more than two pickling segments can be generated. It is decisive that by means of the selective removal of the coating, different coefficients of friction can be generated in the end segment, which meet the different requirements that are provided in functional terms, in particular of the sealing surface and the bearing surface of the flange.

Conveniently, the end segment before the transformation has a bevel on the end surface. In the case of forming an F-shaped flange according to DIN 74234: 1992-09, the outer edge of the pipe is bevelled.

In a preferred embodiment of the invention, the inner tube is made of metal, in particular steel or an alloy of copper and nickel. Preferably, a corrosion protection layer, in particular based on zinc or aluminum, is applied to the inner tube to ensure high resistance to corrosion.

Advantageously, the coating consists of plastic, in particular polyamide. Preferably, the coating has a total layer thickness that is between about 0.05 mm and about 0.4 mm, in particular between about 0.1 mm and about 0.3 mm.

In a preferred embodiment of the invention, the coating is selectively removed by means of a laser beam to peel the end portion. The use of a laser beam allows the elimination of the coating with a high precision and speed of processing. Alternatively or in combination with laser processing, the coating can also be removed by a mechanical process.

Preferably, the coating is completely removed in the first pickling segment. A complete removal of the coating in the first pickling segment takes into account the requirements of the sealing surface formed by the first pickling segment. In particular, the risk of particle detachment, which may affect, for example, the functional safety of a brake system, is avoided. In contrast, the reduction of the layer of the second pickling segment to the second layer thickness is harmless for the operational safety of a braking system, since the contact surface formed by the second pickling segment is on the pick-up side. the flange that is remote from the sealing surface, so that it is discarded, that the particles of the coating can enter the interior of the pipe.

Conveniently, the coefficient of friction generated in the first pickling segment is greater than the coefficient of friction generated in the second pickling segment, in particular, to meet the requirements of the practice, as specified, for example, in the VDA standard. 235-203.

The additional details and advantages of the invention are apparent from the following description of the examples of preferred embodiments. In the drawings that schematically illustrate the embodiments are shown in detail:

Fig. 1a a longitudinal section through a pipe connected to a connection element with an F-shaped flange.

Fig. 1b a longitudinal section corresponding to Fig. 1a with a flange of the form E;

Fig.1c a longitudinal section through an E-F connection.

Fig.1d a longitudinal section through an F-F connection.

Fig.2a a longitudinal section through a pipe before the pickling of the end segment.

Fig.2b a longitudinal section through the pipe according to Fig.2a after the pickling of the end segment;

Fig.2c a longitudinal section through the pipe according to Fig.2b after the provision of a bevel on an end surface of the end segment;

Fig.2d a longitudinal section through the pipe according to Fig. 2c after the formation of the end segment to a bevel in the form of F;

Fig.2e a longitudinal section through a pipe according to Fig. 2b after forming the end segment to an E-shaped flange and

3 shows an enlarged view of the longitudinal section of FIG. 2b.

The embodiment shown in Figure 1a comprises a pipe 10 which is fixed by means of a pipe screw 60 to a connecting element 50, which is, for example, a brake system unit of a motor vehicle. The connecting element 50 has an opening 51, which opens in a pipe 52. The opening 51 has an internal thread 53 and a connecting surface 54 located at the bottom of the opening 51, which surrounds the pipe 52 and is concave in the present case. The pipe screw 60 has an external thread 61 which is screwed into the internal thread 53 of the connecting element 50. The pipe screw 60 also has a contact surface 62 which is located in the axial direction x forward.

The pipe 10 that serves as the brake pipe has an inner pipe 20 consisting of copper or nickel alloy, on which a corrosion protection layer 21 is applied, as shown in particular in figure 3. The protective layer against corrosion 21, which ensures a high resistance to corrosion at relatively high temperatures is, for example, a zinc layer or an aluminum-zinc alloy. As can also be seen in figure 3, on the corrosion protection layer 21 there is a coating 30 that surrounds the inner tube 20, which consists of plastic, in particular polyamide. The coating 30 has a total layer thickness A ^b that is between about 0.05 mm and about 0.1 mm, in particular between about 0.1 mm and about 0.3 mm.

The pipe 10 has, as shown in FIG. 3, an end segment 12 that opens on an end surface 11 in the axial direction x. The end segment 12 is deformed into a flange 40, which has a front sealing surface 41 in the axial direction x and a sealing surface 41 that faces outwardly from the bearing surface 42, as shown in particular in Fig. 2d . The flange 40 corresponds to the shape F according to DIN 74234: 1992 09, whereby the sealing surface 41 is configured convexly. In the installed state, the sealing surface 41 convex against the concave connection surface 54 is fluid-tight, as can be seen in Figure 1a. The contact surface 62 of the pipe screw 60 lies against the bearing surface 42. The pipe 10 is thus held by means of the flange 40 between the contact surface 62 and the connecting surface 54.

The embodiment shown in figure 1b comprises a pipe 10 which is fixed by means of a pipe screw 60 to a connecting element 50. However, unlike the embodiment according to figure 1a, the flange 40 does not correspond to the shape F, but corresponds to form E according to DIN 74234: 1992-09. Therefore, the sealing surface 41 is designed concavely and in contact with the connecting surface 54 of the connecting element 50, which is convex in this case liquid-tight. It can also be seen that the contact surface 62 of the screw of the pipe 60 bears against the contact surface 42 of the flange 40. The pipe 10 is supported by means of the flange 40 between the contact surface 62 and the surface connection 54 as well as in the embodiment of Fig. 1a.

The embodiment shown in Fig. 1c refers to the so-called E-F connection in which the pipe 10 is connected by a tube nut 80 which includes a contact surface 81 with an additional pipe 70. The pipe 70 has a flange 40a of the form E, while the pipe 10 has a flange 40 of the form F. The sealing surface 41 of the flange 40 of the pipe 10 is designed convexly and in contact with the surface of concave contact forms a sealing surface 41a of the flange 40a of the liquid-tight conduit 70. The contact surface 62 of the screw of the pipe 60 abuts against the bearing surface 42 of the flange 40, while the contact surface 81 of the pipe nut 80 bears against the bearing surface 42a of the flange 40a. The pipe 10 and the pipe 70 are thus held by means of the flange 40, 40a between the contact surface 62 and the contact surface 81.

A so-called FF connection, which is shown in Figure 1d, comprises a pipe 10, which is connected by means of a pipe nut 80 to an additional pipe 70. In contrast to the embodiment according to Figure 1c, both pipe 10 and the pipe 70 each have an F-shaped flange 40, 40a. In order to allow a liquid-tight connection of the pipe 10 with the pipe 70, between the pipe 10 and the pipe 70 is an intermediate element 90, which it has connecting surfaces 91, 92 concave. The convex sealing surface 41 of the flange 40 bears against the concave connection surface 91 of the intermediate element 90 in a fluid-tight manner. The convex sealing surface 41 of the flange 40 bears against the concave connection surface 91 of the intermediate element 90 in a fluid-tight manner. Also, the convex sealing surface 41a of the flange 40a abuts the concave connection surface 92 of the intermediate element 90 in a liquid-tight manner. As in the case of the embodiment according to Figure 1c, the contact surface 62 of the screw of the pipe 60 bears against the bearing surface 42 of the flange 40 and the contact surface 81 of the pipe nut 80 against the contact surface 42a of the flange 40a. The pipe 10 and the pipe 70 are thus fastened by means of the flange 40, 40a and the intermediate element 90 between the contact surface 62 and the contact surface 81.

To ensure that during the screwing of the pipe screw 60 there is no torsion of the pipe 10, 70 and, optionally, the intermediate element 90, which can optionally lead to an undesirable torsional tension in the pipe 10, 70 and the intermediate element 90, it is desirable that in the area of contact between the contact surface 62 and the abutment surface 42, and, optionally, in the area of contact between the contact surface 81 and the abutment surface 42a, which is indicated in Figs. 1a to 1d with I, relatively low friction occurs. In the region of contact between the sealing surface 41, 41a and the connecting surface 54, 91, 92, which is pointed out in

Fig. 1a to 1d with II, however, it is advantageous that a comparatively high amount of friction is produced, in particular, ensuring a liquid-tight connection of the pipe 10 with the connecting element 50, the intermediate element 90 or the other pipe 70. To meet these different requirements, the surface of the sealing surface 41, 41a is such that a first coefficient of friction pi results. The surface of the bearing surface 42, 42a, however, is such that a second coefficient of friction p2 results, which is smaller than the first coefficient of friction | J1.

The production of said pipe 10, 70 is shown in Figures 2a to 2e. Figure 2a shows the pipe 10 provided comprising the inner tube 20 extending in the axial direction x, the layer of protection against corrosion

21 applied to the inner tube 20 and the liner 30 in the corrosion protection layer 21 surrounding the inner tube 20.

After providing the pipe 10, 70 the coating 30 in the end segment 12 is removed in known manner by means of laser processing or mechanical treatment, for example by means of a pickling tool, or by a combination of both. As can be seen in Figure 2b, the end segment 12 is removed along a first pickling segment 13 such that the surface of the end segment 12 in the first pickling segment 13 causes the first friction coefficient | J1 . The first stripping segment 13 extends in the axial direction x from a first initial point 14 located on the end surface

11 to a first end point 15. The end segment 12 is removed in such a way that the surface of the end segment 12 in the second pickling segment 16 causes the second coefficient of friction p2, which is smaller than the first friction coefficient | J1 . The second pickling segment 16 extends in the axial direction x from a second starting point 17, which in this case coincides with the first end point 15 to a second end point 18, which forms the end of the end segment 12. To manufacture the different coefficients of friction and

P2, the coating 30 is reduced in the first pickling segment 13 to a first layer thickness A1 and in the second pickling segment 16 to a second layer thickness A2 which is greater than the thickness of the first layer A1, as shown in Fig. 3. The first layer thickness A1 is preferably zero, that is, the coating 30 is completely removed in the region of the first pickling segment 13.

After the selective removal of the coating 30 in the end segment 12, the outer edge of the end surface 11 may be provided if necessary with a bevel 19, as seen in Fig.2c. Subsequently, the end segment 12 is deformed to form the flange 40, for example, by means of a conventional clamping tool. The flange 40 shown in Figure 2d, corresponds to the shape of F according to DIN 74234: 1992-09, but can also be obtained in the form of E, as shown in the Figure

2e. It is decisive that the end segment 12 be deformed in such a way that the first pickling segment 13 forms the sealing surface 41 and the second pickling segment 16 forms the bearing surface 42 of the flange.

The procedure described above for manufacturing a pipe 10, 70 provided with the flange 40, 40a, makes it possible to impart a condition corresponding to the respective requirements to the sealing surface 41, 41a and the bearing surface 42, 42a. The comparatively low coefficient of friction p2, which results in the area of the bearing surface 42, 42a by removing the coating 30 to the second layer thickness A2, counteracts the torsion of the tube 10 when the pipe screw 60 is screwed. The complete removal of the coating 30 in the first pickling segment 13 provides the sealing surface 41, 41a, not only to give the required tightness to the liquids with the sealing surface of 54, 91, 92, but also generates a coefficient relatively high friction, which also counteracts the torsion of the pipe 10 when screwing the pipe screw 60. The pipe 10 produced by the selective removal of the coating 30 in the end segment 12 is characterized by a no less important assembly that prevents the appearance of torsional stresses in the pipe 10 and, therefore, counteracts the involuntary detachment of the pipe screw 60 in the installed state.

List of references

10 Pipe

11 Extreme surface

12 Extreme segment

13 First pickling segment

14 First starting point

15 First extreme point

16 Second pickling segment

17 Second starting point

18 Second extreme point

19 Bevel

20 Inside tube

21 Layer of protection against corrosion

30 Coating

40 Flanges

41 Sealing surface

41a Sealing surface

42 Support surface

42a Support surface

50 Connection element

51 Opening

52 Line

53 Internal thread

54 Connection surface

60 Pipe screw

61 External thread

62 Contact surface

70 Pipe

80 Tube Nut

81 Contact surface

90 Intermediate element

91 Connection surface

92 Connection surface

I Contact area with comparatively low friction II Contact area with comparatively high friction x Axial direction

Ab Total thickness of the layer

A1 First layer thickness

A2 Second layer thickness

First coefficient of friction

P2 Second coefficient of friction

Claims (11)

1. Method for manufacturing a pipe (10, 70) provided with a flange (40, 40a), in particular a brake line or fuel line to a motor vehicle, comprising the following process steps: providing a pipe (10, 70) comprising an inner tube (20) extending in an axial direction (x), a covering (30) covering the inner tube (20) and an end segment (12) ending in an end surface (11) of the pipe (10, 70); performing a pickling on the end segment (12) along a first pickling segment (13) until reaching a first layer thickness (Ai) so that the surface of the end segment (12) produces a first pick-up coefficient. friction (J1) in the region of the first pickled segment (13); performing a pickling in the end segment (12) along at least a second pickling segment (16) to a second constant layer thickness (A2) that is greater than the thickness of the first layer (A1), so that the surface of the end segment (12) produces a second friction coefficient (J2) in the region of the second coating segment (16) which is smaller than the first coefficient of friction (J1); forming the end segment (12) to form a flange (40, 40a) having a sealing surface (41, 41a), on the front side, and a bearing surface (42, 42a) remote from the sealing surface (41 , 41a), such that the first pickling segment (13) forms the sealing surface (41, 41a) and the second pickling segment (16) forms the support surface (42, 42a), the transition from the first pickling segment (13) to the second pickling segment (16) in the region of the largest outer diameter of the flange (40, 40a). 2. Process according to claim 1, wherein the first segment pickling (13) extends in the axial direction (x) from a first starting point (14) to a first end point (15) and wherein the second segment pickling (16) extends in the axial direction (x) from a second initial point (17) to a second end point (18), preferably being the first starting point (14) located on the end surface (11) and also coinciding preferably the first end point (15) and the second starting point (17). 3. Process according to claim 1 or 2, wherein the end portion (12) is optionally provided with a chamfer (19) on the end surface (11) before forming. 4. Process according to any one of claims 1 to 3, wherein the inner tube (20) is made of metal, in particular steel or an alloy of copper and nickel, preferably applied to the inner pipe (20) a layer of protection against corrosion (21), in particular based on zinc or aluminum. 5. Process according to any of claims 1 to 4, wherein the coating (30) is made of plastic, in particular polyamide, having the coating (30) preferably a total layer thickness (Ab) that is between about 0 , 05 mm and approximately 0.4 mm, in particular between approximately 0.1 mm and approximately 0.3 mm. 6. Process according to any one of claims 1 to 5, characterized in that for etching the end segment (12), the coating (30) is selectively removed by a laser beam. 7. Process according to any one of claims 1 to 6, wherein the coating (30) is completely removed in the region of the first segment pickling (13). 8. Pipe, in particular a brake line or fuel pipe for a motor vehicle, comprising: an inner tube (20) extending in an axial direction (x); a covering (30) covering the inner tube (20) and an end segment (12) terminating on an end surface (11) of the pipe; the end segment (12) comprising a flange (40, 40a) having a sealing surface (41, 41a) on the front side and a bearing surface (42, 42a) opposite the sealing surface (41, 41a); the coating (30) being in the region of the end segment (12) selectively removed so that the surface of the end segment (12) produces a first coefficient of friction (J1) on the sealing surface (41, 41a), which is formed by a first pickling segment (13) of the end segment (12), and produces a second friction coefficient (J2) on the support surface (42, 42a), which is formed by a second pickling segment (16) of the end segment (12), the second friction coefficient (IJ2) being smaller than the first coefficient of friction (J1); having reduced in the area of the first pickling segment (13) the coating (30) to a thickness of the first layer (A1) and in the region of the second pickling segment (16) at a constant thickness of the second layer (A2) ) which is greater than the thickness of the first layer (A1), and the transition from the first pickling segment (13) to the second pickling segment (16) located in the region of the largest external diameter of the flange (40, 40a). 9. Pipe according to claim 8, characterized in that the inner tube (20) is made of metal, in particular of steel or of a copper-nickel alloy, preferably applying to the inner tube (20) a layer of protection against corrosion ( 21), in particular based on zinc or aluminum ,. 10. Pipe according to claim 8 or 9, characterized in that the covering (30) is made of plastic, in particular of polyamide, the covering (30) preferably having a total layer thickness (Ab) that is between approximately 0.05 mm and about 0.4 mm, in particular between about 0.1 mm and about 0.3 mm. A pipe according to any of claims 8 to 10, characterized in that the coating (30) is completely eliminated in the area of the first pickling segment (13).